The present invention generally relates to shrink wrap packaging and apparatus and methods for producing the same and particularly to shrink wrap packaging and apparatus and methods for feeding, perforating and cutting a shrink wrap film utilized in producing the shrink wrap packaging.
In shrink wrapping, a single sheet of shrink wrap film is wrapped around the product and into a tubular form. The overlapping lateral edges are located beneath the product and are sealed or otherwise joined together. During shrinking in a heat tunnel, the longitudinal edges of the shrink wrap film collapse against the ends of the product creating bulls eye-type openings.
Various deficiencies exist in prior shrink wrap packaging and the methods of its fabrication. One such deficiency is that the single sheet of shrink wrap film was typically cut from a supply roll of the film. A common manner to cut the sheet from the web of film was to engage the film with a hot iron to melt the film and thus sever the sheet from the film. This hot iron is a high wear component and is always a source of operational problems. Another approach is to utilize a rotary cutter which cuts the film. However, this approach experienced problems that the new leading edge of the web of film did not continue to follow the desired path of the film as a result of the velocity of the film and air resistance, the memory of the film, and/or the snap back of the film when the tension was released on the film because of cutting. These problems were overcome by cutting the film while the film is held across the cut and/or by including mechanical devices which grasp and pull the new leading edge, but such approaches unduly complicated the construction of the apparatus.
U.S. Pat. No. 5,771,662 represents a major advance in the field of feeding, perforating and cutting a shrink wrap film. Specifically, methods and apparatus are disclosed in U.S. Pat. No. 5,771,662 for forming a single sheet of film from a web of film and connected to the web of film by tie strips to maintain tension on the web of film after cutting, with the tie strips later being broken to separate the single sheet of film from the web of film.
However, problems have been encountered with narrow or stretchy film. If the web of film is too tight when the knife cuts the film, it tends to snap apart. This “whip back” causes the lead edge of the next sheet to have folded corners or a lack of tension for the next cut. If the web of film is too loose, the film will not be completely cut and a jam will result. A folded corner can also cause a jam as the film will not be delivered through the opening to the product.